With a display device that uses current drive type light emitting elements, such as an organic EL element (OLED), a driving transistor is normally arranged in a pixel circuit. A display is operated by driving the driving transistor based on display signals. However, because OLED is a current driven element, variable output current of the driving transistor is directly connected to a deterioration of visual quality. Therefore, a wide variety of proposals have been made to control variable driving current for example as in patent reference 1.